Metal Nanoridges in Hollow Si-Loaded Plasmonic Waveguides for Optimal Mode Properties and Ultra-Compact Photonic Devices

To achieve subwavelength mode confinement, we propose a hybrid plasmonic waveguide consisting of a metal nanoridge embedded in a silica-covered hollow silicon ridge waveguide on a metal substrate. The mode confinement, propagation length, and figure of merit are optimized by controlling the geometry of the waveguide. At the optimal figure of merit, the normalized mode area of 3.0 × 10^-3 (λ²/4) is achieved while retaining a propagation length of 163.0 μm at the telecom wavelength of 1550 nm. The coupling strength of a directional coupler composed of two such waveguides is analyzed to examine the degree of integration of photonic integrated circuits. A strong dependence on the coupling length makes the proposed structure very favorable for use in various plasmonic devices. Furthermore, transmission through a 90° bend (studied to examine the compactness of the proposed waveguide), is observed to be 80% at the small radius of curvature of 0.7 μm.